Hygroscopic polymers, such as nylon polymers, have a high affinity for water due to polar bonds in such polymers (e.g., polar amide bonds in the case of nylon polymers). Typically, such polymers may hold approximately 1.5 to 2 percent of their weight in water. However, this weight percentage may be substantially higher if the polymer is stored at high humidity or is immersed in water. Controlling the water content in hygroscopic polymers, such as nylon polymers, is important not only during manufacturing (e.g., via injection molding) but also in the final article of manufacture. Other examples of hygroscopic polymers include acrylonitrile butadiene styrene (ABS) polymers, acrylics, polyurethanes, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT), among others.
Prior to injection molding, resin pellets are dried in order to mitigate problems associated with the presence of water, such as chain degradation, decreased molecular weight, and ultimately degraded mechanical properties in the final article of manufacture. Therefore, understanding the moisture content of the resin pellets is important. While drying the resin pellets is important prior to injection molding, the presence of at least some moisture in the final article of manufacture may be desirable in some cases (e.g., for toughness and/or flexibility). In hygroscopic polymers, water acts as a plasticizer, spacing out the polymer chains, reducing the glass transition temperature, and making the article of manufacture more flexible. Accordingly, after manufacture, a nylon article may be moisture conditioned or allowed to reach its equilibrium moisture content before being used in applications where high loads are generated. Otherwise, brittle fracture of the nylon article may result. Furthermore, depending on the environment, a nylon article may dry out over time, potentially resulting in future failure of the nylon article after field deployment. As such, monitoring of moisture content in the final article after field deployment may also be required in order to prevent the possibility of failure as a result of the article drying out (e.g., in a high temperature and/or low humidity environment).